The Coiled Spring: How Life Begins

Ethan Bier

An introduction to developmental biology, The Coiled Spring is a
textbook aimed at students that may appeal to a broader audience.
It assumes only the most basic genetics — genes, the Central Dogma,
transcription, translation, and regulation — and even that is explained
in the first chapter. And chapter two introduces the basic toolkit of
the geneticist studying development — recombinant DNA, gene cloning,
in situ hybridization, and mutants.

The core of The Coiled Spring consists of six chapters, two on each of
fruit flies, vertebrates, and plants. The first chapter in each pair
covers the determination of the primary axes in embryos (how animals
initialise their anterior/posterior and dorsal/ventral structure, and
plants their apical/basal and radial patterning). The second looks at
the formation of appendages — wings and eyes in flies, limbs and eyes
in vertebrates, and flowers and leaves in plants. Bier makes no attempt
to be systematic here, instead using a few detailed examples to explain
the basic mechanisms involved — division into increasingly specialised
domains, morphogens and induction, autoactivation, mutual inhibition,
and so forth.

The details in all of this are superficially intimidating, with lots of
strange gene names (sonic hedgehog, pax6, agamous, and so forth)
and other specialised terminology (mesoderm and ectoderm and endoderm,
organizers and neuroblasts, marginal zones and meristems, and so forth).
But the key ideas are not that difficult and they are explained multiple
times in different contexts. In addition to an overall glossary, lists
of key terms and important genes accompany each chapter. The Coiled
Spring also has exceptionally clear colour diagrams (as well as a couple
of pages with small photos from actual experiments). Bier has a fondness
for analogies with household electronics, which are interesting if not
always helpful. He also includes almost a score of "bioboxes", with a
page or two on the careers of key biologists involved with developmental
biology; these are professional rather than personal.

The Coiled Spring doesn't look at all at later stages of development,
but it does cover the fascinating evolutionary angle in some depth.
Vertebrates and invertebrates share a common developmental inheritance —
only a decade ago it was discovered that some vertebrate homeotic genes
can even substitute for fly ones! And from a comparative analysis we
can deduce that their last common ancestor probably had "a well defined
head and tail", "repeated segments", "basic tissues types", "some kind
of appendages or outgrowths", and "a light sensitive organ". There are
also connections between plant and animal development, though these may
result more from general constraints on the mechanisms available rather
than direct common descent.

A final chapter looks at some of the broader implications of advances
in genetics and developmental biology. Health and medical improvements
are what spring to mind, but Bier stresses the effects on agriculture and
other forms of plant production (and he gives his own take on genetically
modified organisms). Heading more towards science fiction, he considers
the possibilities of Jurassic Park style revivals, crossing species,
and targeted evolution.